Atrial fibrillation (AF), which is the name for rapid beats in the upper chambers of the heart, is the world's most common kind of irregular heart beat. People with AF experience symptoms such as heart palpitations (a racing or pounding feeling in the chest), shortness of breath, dizziness, fatigue or weakness. Although AF can occur in otherwise healthy people for no apparent reason, it is sometimes associated with high blood pressure, heart disease or lung problems. The purpose of the SAFARI trial is to study the effectiveness of pacing algorithms in the upper chamber of the heart for patients who have both AF and bradycardia (slow heart beat).

Inclusion Criteria:

• Subjects with a slow heartbeat who are in need of dual chamber pacing (pacing in both the atrium and ventricle).
• Subjects who have experienced at least two episodes of rapid heart beats three months prior to enrollment.

Exclusion Criteria:

• Subjects who have a history of permanent (chronic) or persistent (non self-terminating) atrial fibrillation.
• Subjects with atrial fibrillation due to reversible cause, (e.g. thyroid disease, pericarditis, post-surgery, alcohol abuse).
• Subjects with a history of one or more cardioversions (changing an abnormal heart rhythm into a normal one by either using medication or by the application of an electric shock) six months prior to enrollment.